Intracavitary endoscopic electrosurgery is useful for treating tissue in anatomical or surgically created cavities of the body which can be accessed by methods involving minimal trauma to the patient, be this through a natural body passage or one created artificially. The cavity is distended to provide space for gaining access to the operation site to improve visualisation and to allow for manipulation of instruments. In low volume body cavities, particularly where it is desirable to distend the cavity under higher pressure, liquid rather than gas is more commonly used due to better optical characteristics and because it washes blood away from the operative site. Conventionally, a non-electrolyte solution such as glycine is used as the fluid distension medium when electrosurgery is being used, glycine being electrically non-conductive.
The limited surgical access encountered during intracavitary endoscopic procedures makes the removal of tissue pieces derived from a typical electrosurgical loop cutting electrode both difficult and time consuming. Vaporisation of tissue whereby the tissue is reduced to smoke and water vapour is a preferable technique in these situations, rather than the piecemeal removal of tissue. The products of vaporisation may be removed following dissolution within a liquid irrigating medium.
With regard to underwater endoscopic electrosurgery, the applicants have found that it is possible to use a conductive liquid medium such as normal saline in place of glycine. Normal saline is the preferred distension medium in underwater endoscopic surgery when electrosurgery is not contemplated or a non-electrical tissue effect such as laser treatment is being used. Although normal saline (0.9%w/v; 150 mmol/l) has an electrical conductivity somewhat greater than that of most body tissue, it has the advantage that displacement by absorption or extravasation from the operative site produces little physiologicai effect and the so-called water intoxication effects of glycine are avoided.
Effective electrosurgical treatment of tissue which is totally immersed in liquid at the application site is difficult to achieve because the heat generated by the flow of electrical currents in both the tissue being treated and surrounding conductive liquid tends to cause boiling of the liquid. The operating electrode is intermittently surrounded by water vapour rather than liquid, with consequent large variations in the electrical impedance of the load presented to the generator supplying the electrosurgical power to the electrode. Whilst this variation is mitigated by use of a non-conductive liquid, it cannot be eliminated entirely due to the release of body fluids at the operative site which elevates the electrical conductance of the liquid. Changes in tissue type also alter the load impedance. These effects result in difficulty in controlling the electrosurgical output to produce consistent effects on the tissue being treated. As a result, high powers are commonly employed to overcome this performance variation.